Telephonic receiver



Aug. 11.,A 1925. 1,549,131

E. A. GRAHAM TELEPHONI C RECEIVER Filed Jan. 19, 1925 Ea/arci Jlfred raham his ttorney Patented Aug. 11, 1925.

UNITED STTES EDWARD ALFRED GRAHAM, OF BROCKLEY, LONDON, ENGLAND.

TELEPHONIC RECEIVER.

Application filed January 19, 1925.

To all whom t may concern.'

Be it known that I, EDWARD ALFRED Graa- HAM. a subject or' the King of Great Britain and Ireland, residing at Brockley, in the county ot London, England, have invented Improvements in or Relating to Tclephonic Receivers (for which I have filed application in Great Britain, August 29, 1923, No. 21,834), of which the following is a speciiication.

IVhen using wireless receivers and like apparatus embodying thermionic valves, it is necessary, in order tocobtain the best result, that a telephonie receiver should be selected or adapted to suit the type ot valve, of the last valve in a set of valves, used. Thus, when using a low power valve, which has a high impedance, a telephonic receiver should be used having a high impedance, whilst when a high, power valve is used, which has a relatively low impedance, a telephonic receiver should be used having a relatively low impedance.

Now the present invention has for its object to provide a telephonie receiver that can be readily adapted, at will, for use either with a low power valve or a high power valve.

For this purpose, a telephonie receiver of the kind having, as usual, only two main terminals, is provided with multiple windings and with a switch device whereby the windings can be directly connected in series between the two terminals to otler a high resistance when the receiver is to be used with a lower power valve, or can be connected in parallel or, it may be, it' desired, in series parallel between the two terminals, to oi'er a lower resistance when the receiver is to be used with a high power valve. A switch suitable for the purpose described can be variously constructed and be arranged within the telephone casing and be adapted to be operated from the exterior thereof, as by a spindle, lever, push pin or the like, extending through the casing, or the switch may be arranged external to the casing, say at the back thereof.

In the accompanying drawings, Fig. 1 is a diagram illustrative of one arrangement according to the inventionFig. 2 being an exterior view of a receiver embodying suoli an arangement. Fig. 8 is a diagram of another arrangement according to the invention.

Referring iirst to Fig. 1 wherein 1 rep-ref Serial No. 3,388.

sents the diaphragm of a telephone receiver having two coils or windings 2 and 2% the switch comprises four spring blade contacts, a, Z), o and (l, arranged in pairs and a rotary switch member 3 located between the two pairs. Contacts a and d are connected to the ends of winding 2 and contacts b and c to the ends of the second winding 2a, contact a being connected to one terminal 4L of the receiver and located in proximity to contact Z), and contact c being connected to the second terminal 5 of the receiver and located in proximity to contact al. Contacts ZJ and d carry conducting projections adapted to bc pressed against contacts a and c. The rotary switch member 3 is located between contacts Z) and Z and comprises a metal body carrying oppositely arranged projections o of insulating material, the said member being so shaped that in the position shown, contacts b and (Z, which constantly bear against it, are held away from contacts a and c by their spring action and are electrically connected together through the metal body, whilst in a second position, the projections 6 ot insulating material on the said body hold contacts I) and (Z against contacts a and o'. respectively. The arrangement is such that in the illustrated position of the rotary member 3, the receiver windings 2 and 2 are connected in series and in the second posi-- tion of the said member, they are connected in parallel. Such a switch can be made of small size to admit of its being conveniently located within the receiver casing.' Fig. 2 illustrates a telephone receiver A which, as to construction in general, is similar to that disclosed in the speciiication of my former Letters Patent No. 15369 of 1915, 7 representing in full lines a lever Jfor the switch member 3 when occupying the position corresponding to the series connections oi the coils 2 and 2a. Vhen the lever is moved into the dotted line position, the switch member 3 occupies a position corresponding to the coils Q and 2a being connected in parallel. 8, 8fL are stops for the lever.

In the arrangement according to Fig. 3, suitable for use with a telephonie receiver having four windings 9, the switch comprises eight switch levers 10 each associated with three contacts 11 all connected in circuit relationship as will be clearly apparent upon inspection withoutthe necessity of a detailed description. In the irst position, where the levers 10 are represented by full lines, the coils 9 are connected in series between the leads 12, 13 and on the assumption that the resistance of each .coil is 500 ohms then the total resistance will equal 200() ohms.

In the second position oi the levers, represented by dotted lines 10a, the lett hand pair of windings are connected inV series whilst the right hand pair are similarly connected in series, the two resultant pairs being however connected in parallel to aiord a circuit resistance of 500 ohms.

In the third position of the levers, represented by dot and dash lines 10'), all tour windings are connected in parallel so that the resultant circuit resistance is 125 ohms.

The mechanical construction of such a switch may be oi any suitable or known character;

That I claimr is 1. In a telephonie receiver for purposes such as herein referred to, a casing having a pair of main terminals, a magnetic system in such casing, a pair ot windings associated therewith, a rotary switch member within the casing, spring contact members associated with the windings and with the rotary switch member, a lever member outside the vcasing for operating the rotary switch member and stops for such lever adapted to ensure that in one position the windings are connected in series between the main terminals and in another position in parallel therebetween.

2. In a telephonie receiver for purposes such as herein referred to, a casing having a pair of main terminals, a magnetic sys tem in said easing, a plurality of windings associated therewith, a rotary switch member within the casing'and a lever for actuating said switch member whereby the latter may bemoved to eiiect alternative connection oi' the windings inseries and in para1 flel between the terminals.

Signed at London England this seventh day of January 1925.

EDVARD ALFRED GRAHAM. 

